A known electromagnetic actuator includes a supporting member (yoke) which supports an electromagnetic coil around which a wire is wound, a moving member (armature) which is positioned facing the supporting member so as to move forward and backward, an actuating force transmitting member which transmits moving force of the moving member to a member to be actuated as actuating force. According to the known electromagnetic actuator, the moving member is moved towards the supporting member by an effect of magnetic force generated by applying electric current to the electromagnetic coil and the actuating force is provided to the member to be actuated via the actuating force transmitting member. An above-described type of electromagnetic actuator is adopted as a part of an electromagnetic clutch such as a differential. An above-described electromagnetic clutch is adopted as a part of a driving force transmitting apparatus for a vehicle (See JP2003-148517A).
With the construction of the known electromagnetic actuator, although it is required to provide large degree of the actuating force to the member to be actuated in order to properly operate the member to be actuated, a structure which generates large degree of actuating force which is applicable, for example, to a driving force transmitting apparatus for a vehicle by an electromagnetic actuator per se has not been proposed. Accordingly, with construction of a driving force transmitting apparatus described in JP2003-148517A, in order to cope with the foregoing, an actuating force increasing mechanism such as a cam mechanism is adopted to increase the actuating force generated by the electromagnetic actuator and to transmit to a clutch mechanism serving as the member to be actuated.
Notwithstanding, in case the aforementioned actuating force increasing mechanism is adopted to construct an electromagnetic clutch or a driving force transmitting apparatus for a vehicle, the number of parts of the electromagnetic actuator increases and the construction of the electromagnetic actuator becomes complex because of the actuating force increasing mechanism. This brings a drawback that construction of an electromagnetic clutch or a driving force transmitting apparatus for a vehicle become complex and dimensions thereof are increased by applying the actuating force increasing mechanism.
Further, according to the known electromagnetic clutch or the driving force transmitting apparatus for the vehicle having the actuating force increasing mechanism, length of a magnetic path which is formed by applying an electric current to the electromagnetic coil is consequently increased, which increases reluctance, decreases magnetic flux density, and, thus decreases attraction force relative to the moving member (armature). Further, according to the actuating force increasing mechanism and the electromagnetic actuator which includes the actuating force increasing mechanism, there is a drawback that drag torque generated in the actuating force increasing mechanism and the electromagnetic actuator is increased and transmitted to the member to be actuated because of the foregoing structure.
On the other hand, another type of known electromagnetic actuator (electromagnetic coil device) which is devised to be downsized and to generate adequate electromagnetic force has been proposed (See JP2005-188560A). According to the known electromagnetic coil device described in JP2005-188560A, the electromagnetic coil is divided into plural pieces so as to be small, and electrical resistance of the electromagnetic coil is reduced by downsizing the electromagnetic coil, and, thus to exert adequate electromagnetic force. However, the known electromagnetic coil described in JP2005-188560A does not move the moving member by the attraction force of the electromagnetic force, and, thus does not apply the moving force to the member to be actuated via the actuating force transmitting member.
A need thus exists for an electromagnetic actuator which generates large degree of actuating force for properly operating a member to be actuated, an electromagnetic clutch including the electromagnetic actuator, and a driving force transmitting apparatus for a vehicle including the electromagnetic clutch.